Lot Quality Assurance Sampling of Sputum Acid-Fast Bacillus Smears for Assessing Sputum Smear Microscopy Centers

Abstract

Assessment of 12 microscopy centers in a tuberculosis unit by blinded checking of eight sputum smears selected by using a lot quality assurance sampling (LQAS) method and by unblinded checking of all positive and five negative slides, among the slides examined in a month in a microscopy centre, revealed that the LQAS method can be implemented in the field to monitor the performance of acid-fast bacillus microscopy centers in national tuberculosis control programs.Several measures are being undertaken by tuberculosis (TB) control programs worldwide to ensure the quality of sputum acid-fast bacillus (AFB) microscopy services that they provide (9). In India, in accordance with the Revised National Tuberculosis Control Programme (RNTCP) guidelines, all of the positive and five of the negative slides among the total slides examined in a calendar month in a designated microscopy center (DMC) are checked in an unblinded fashion by the senior TB laboratory supervisor (STLS) during his or her onsite supervisory visits (3). Recently, the international guidelines on external quality assessment of sputum AFB microscopy (7) have suggested a lot quality assurance sampling (LQAS) method, which is designed to recheck a minimum number of slides examined in DMCs to identify the faulty centers with an unsatisfactory level of performance. The present study documents the assessment of 12 microscopy centers in a subdistrict by using the two methodologies.Organization. The organization of the RNTCP in India is shown in Fig. 1. Tiruvallur district in Tamil Nadu state has six subdistricts known as TB units (TUs). The Velliyur TU, where the present study was carried out, has 12 microscopy centers: seven DMCs and five non-designated microscopy centers (NDMCs). The collection of sputum samples, staining by a hot Ziehl-Neelsen method, and grading were done according to standard procedures (1). One trained laboratory technician is employed at each microscopy center, and one STLS is responsible for supervision of all microscopy centers, usually five in all, in the respective TUs. Direct sputum smears prepared during April 2002 and March 2003 were included in the study.Unblinded checking. Every month, during on-site supervisory visits to the microscopy centers, the STLS in an unblinded fashion checks all positive smears and five negative smears (2, 3). The percentages of false-positive (any positive read as negative by the STLS) and false-negative (any negative read as positive by STLS) results were calculated. Centers with Ͼ5% error were considered to have systematic problems.Blinded checking using LQAS. In July 2003, all of the routinely examined slides (from April 2002 to March 2003) were brought to the national reference laboratory at Tuberculosis Research Centre (TRC) Chennai for rechecking. From each microscopy center, 8 slides per month (annual total of 96 slides) were systematically selected after the slide number was recorded in the register. The sample size was based on the following considerations: a sensitivity of 80% (i.e., the pe...

Sputum Smear Microscopy: Evaluation of Impact of Training, Microscope Distribution, and Use of External Quality Assessment Guidelines for Resource-Poor Settings

“…Similar to the findings of studies performed in India, the Philippines, and Mexico, we found blinded rechecking and the LQAS strategy to be operationally feasible (3)(4)(5)(6). The blinded rechecking identified those laboratories with a high number of smear microscopy errors and allowed the distinction between those laboratories with optimal and suboptimal performance.…”

“…To decrease the EQA workload, the blinded rechecking recommendations incorporate statistical sampling methods developed for industrial quality control. To date, few countries have implemented the 2002 EQA guidelines and few studies have evaluated the routine implementation of these new guidelines in resource-poor settings (3)(4)(5)(6).…”

External quality assessment in resource–limited countries

“…Selvakumar et al reported rechecking of 8 slides per month per microscopy centre was sufficient to assess performance of sputum smear microscopy in 12 centres in one district in India, based on sensitivity of 80%, specificity of 100%, slide positivity rate of 10% and annual negative smear volume of 1000–5000 slides. ( 44 ). They also noted the discrepancy between microscopy centres and district supervisors was higher (4.7%) than with the reference laboratory (1%), suggesting lack of training and motivation at district level ( 45 ).…”

External quality assurance for the laboratory diagnosis of Buruli ulcer disease in Ghana

“…Further sampling for EQA could be performed according to the Lot Quality Assurance System (LQAS) as recommended in the international EQA guidelines. Experiences from several countries proved already the suitability of LQAS for implementation in the field (Selvakumar et al. , 2005).…”